There is a steadily increasing demand for technology capable of converting discarded and waste plastic materials into higher value products. This is due in large measure to public concern over potential environmental damage caused by the presence of such waste materials. Plastics waste is the fastest growing waste product, with about 30 million tons in 2009, compared to 18 million tons in 1995 and only 4 million tons in 1970. This amount is growing at more than 10% per year. In 2009 the 30 million tons of plastic waste represented about 12 wt. % of total municipal solid waste (MSW). Transforming plastic waste material into useful products presents a unique opportunity to address the growing environmental concerns
Of the 30 million tons of waste plastics in 2009, about 13 million tons was in the form of containers and packaging, about 11 million tons was in the form of durable goods, such as appliances, and about 7 million tons was in the form of non-durable goods, such as plates, cups, etc. While great effort is being made to recover and recycle as much waste plastics as possible, there are various challenges that must be met for cost effective recycling. For example, waste plastics are typically composed of a variety of different plastic types, some of which are not compatible with one or more other types depending on the desired end products. For example, when different types of plastics are melted together they tend to phase-separate and set into layers. The phase boundaries between layers lead to structural weakness in the resulting blend of material, thus, such reconstituted polymer blends are only useful in limited applications. Another barrier to recycling of plastics is the widespread use of dyes, fillers and other additives used in the manufacture of the original plastic products. A melt of plastics waste is generally too viscous to economically remove fillers, and would be damaged by many of the processes that could potentially remove the added dyes.
One use for waste plastics that can add to the alternative energy pool is to convert at least a fraction of the waste plastics to a hydrocarbon transportation fuel, such as a gasoline, diesel fuel, etc. There is an increasing demand for alternative energy sources and transportation fuels. While a mixture of waste plastic types can, in general, be used as a feedstock for its conversion to transportation fuels, any polyvinyl chloride (PVC) or polyethylene terephthalate (PET) plastics material component of the plastics feedstock will have to be kept to a minimum. When PET and/or PVC is included in the feedstock acids are formed that can result in corrosion of metal parts of processing equipment and to an acidized oil product.
Although there are myriad processing schemes for producing transportation fuels from non-petroleum sources, as well as myriad processing schemes for recycling waste plastics, there is still a need in the art for processes that are capable of converting waste plastics to higher value products in a cost effective manner.